However this one might have abit too much work behind it with scripting and making it balanced between all the classes.
However the idea behind is that it has a small twist! Your the only defender so its not really a tower defence. My idea was having ppl running around killing running enemys (that dont attack nor give loot) and evry 10 levels you go up vs a boss. However i think it might be only for Warriors and rangers, or while doing this mages will be gaining mana all the time. But like i said before i got a feeling this might be fairly hard to script or its really easy. But finding a balance between the classes is maybe one of the problems. Anyway just an idea im tossing out there to see what comments i might get!